Keywords
amniocentesis - chorionic villus sampling - fetal blood sampling - prenatal ultrasound
Introduction
Diagnostic puncture is an essential part of prenatal diagnostics and makes it possible
to
acquire cells from the fetus and placenta so that they can be examined with respect
to the
relevant medical issue (microscopic and molecular karyotyping, molecular genetic analysis
of
monogenic diseases, infections, hematological diagnostics, etc.). Puncture is currently
the
only established and sufficiently scientifically evaluated option for diagnosing genetic
diseases based on pregnancy-specific cells.
In 2013, the Section of Gynecology and Obstetrics of the German Society for Ultrasound
in
Medicine (DEGUM) published recommendations on diagnostic puncture in prenatal medicine
[1].
The developments and new findings in recent years make it necessary to revise and
reformulate these recommendations. The acceptance and number of diagnostic punctures
in
Germany, as in other countries, has fallen significantly largely due to the introduction
of
first-trimester screening and the analysis of cf-DNA (cell-free DNA) from maternal
blood
(noninvasive prenatal test – NIPT) ([Table 1]). According to data from the National Association of Statutory Health Insurance
Physicians, the total number of amniocentesis and chorionic villus sampling (CVS)
procedures
in Germany in the period from 2003 to 2020 in relation to the number of births decreased
from
8.3% to 1.5%. The number of amniocentesis procedures decreased significantly more
than the
number of chorionic villus sampling procedures. Fetal blood sampling (FBS) comprises
only a
small portion of punctures (326 in 2019).
Table 1 Number of diagnostic punctures in prenatal medicine calculated according to the
uniform value scale and live births per year in Germany (source: statistics of the
National
Association of Statutory Health Insurance Physicians and the Federal Statistical Office
of
Germany).
|
Fee schedule item
|
2003
|
2013
|
2015
|
2017
|
2019
|
2020
|
|
01781 – amniocentesis
|
54,393
|
17,809
|
12,330
|
9,265
|
7,163
|
7,182
|
|
01787 – CVS
|
4,493
|
4,611
|
4,101
|
4,112
|
4,084
|
4,284
|
|
Total
|
58,886
|
22,420
|
16,431
|
13,377
|
11,247
|
11,466
|
|
Births
|
706,721
|
682,069
|
737,575
|
784,901
|
778,100
|
773,100
|
|
Percentage of amniocentesis + CVS
Per birth
|
8.3%
|
3.3%
|
2.3%
|
1.7%
|
1.4%
|
1.5%
|
The decreased demand for diagnostic puncture is due to changes in diagnostic options.
Today, puncture is primarily performed due to abnormal sonographic findings in the
first,
second, and third trimester as well as due to first-trimester screening and cf-DNA
analysis
results requiring clarification.
On the other hand, numerous studies and meta-analyses were able to show that the risk
of
miscarriage after diagnostic puncture is very low at expert centers and does not differ
from
the natural risk of miscarriage [2]
[3]
[4]
[5].
In addition, knowledge of the incidence and the clinical picture of genetic diseases
that
can be diagnosed after puncture using molecular-genetic techniques (microarray and
exome
analysis) and karyotyping has increased exponentially in recent years. Many of these
diseases
are not detected by ultrasound or currently available cf-DNA tests. The requirements
for the
informed consent discussion and counseling regarding these complex correlations have
thus
increased significantly.
The term “invasive diagnostic testing”, which was commonly used for a long time to
refer
to amniocentesis, CVS, and FBS, has had a negative connotation for a few years. Instead,
the
term “diagnostic puncture” is used in the following and is intentionally juxtaposed
with the
term “NIPT” (noninvasive prenatal testing). In this text NIPT refers to cf-DNA analysis
(cell-free DNA analysis) [6].
The recommendations provided in the following are intended to provide information
about
all relevant aspects of diagnostic puncture in prenatal medicine.
The goal of this review article is to provide important and current facts regarding
puncture in prenatal medicine (techniques, complications, genetic testing). It is
intended to
provide basic, comprehensive, and up-to-date information on diagnostic puncture in
prenatal
medicine and is written for physicians and other persons who provide medical care
for pregnant
women and do not have their own puncture experience.
According to the authors of this article, there is no similar up-to-date compendium
of
diagnostic puncture procedures in prenatal medicine for colleagues receiving puncture
training.
Physicians with puncture experience will find here the currently valid rules for puncture,
the current complication numbers, and an overview of the options for genetic testing.
These guidelines for diagnostic puncture in prenatal medicine replaces the version
from
2013 [1].
Gestational age
Chorionic villi sampling: starting at 11 + 0 gestational weeks
Amniocentesis: starting at 15 + 0 gestational weeks (or only if
there is fusion of amnion and chorion, i.e., possibly also later). Cordocentesis: starting at 20+0 gestational weeks, or earlier in exceptional cases
[7].
All techniques can be used starting at the gestational ages mentioned above over the
entire course of the pregnancy. The following aspects must be taken into consideration:
In the case of puncture of the placenta in the second and third trimesters (placental
biopsy), fewer villi than in the first trimester are usually aspirated and less mitotic
activity is seen in the individual villi. Evaluation is thus more difficult due to
the changes
in the differentiation of the villi [8]. Therefore, after 20+0 weeks, cordocentesis should be considered.
However, it should always be taken into consideration that the selected puncture method
can vary based on indication. Therefore, in cases of doubt, the method should be selected
in
consultation with a human genetic council.
Potential indications and possible laboratory tests
The indications for amniocentesis (AC) and CVS are largely the same ([Table 2]). In addition, hematological features of the fetus (e.g. hemoglobin and platelet
count) can be examined with FBS.
Table 2 Possible indications for diagnostic puncture according to [6] and [1] * See below for explanation.
|
1. Increased risk for fetal chromosomal aberration or monogenic disease
-
Fetal deformities
-
Growth restriction (particularly early)
-
Increased risk after first-trimester screening
-
Increased nuchal translucency *
-
Abnormal biochemical findings in first-trimester screening PAPP-A < 0.2
MoM or f-ßHCG < 0.2 or > 5 MoM [9]
[10]
-
Abnormal cf-DNA screening findings
-
Chromosomal aberrations in the parents
|
|
2. Increased risk for a known familial genetic disease
-
Familial genetic diseases with known mutations
-
Genetic metabolic diseases
-
Prior pregnancies with genetic abnormalities
-
Carrier status of the pregnant woman for a disease with X-chromosome
inheritance
-
Carrier status of both parents for an autosomal-recessive genetic
disease
|
|
3. Diagnosing an infection
|
|
4. Wishes of the pregnant woman
|
Today, it is possible to detect approximately half of complex malformations between
11
and 14 gestational weeks [11]
[12].
Due to the strong association between fetal malformations and genetic diseases,
additional attempts are being made to detect these earlier and with greater
frequency.
In the case of fetal malformations and intrauterine growth restriction with
malformations, pathological karyograms are seen in 9–30% of cases with conventional
cytogenetic examination depending on the indication [13]
[14]. Even if the classic trisomies 21, 18, and 13 comprise the majority of cases, other
chromosomal abnormalities must also be taken into consideration.
Therefore, in a large study including approximately 130,000 fetuses with unremarkable
ultrasound, pathological karyograms were seen in 1.6% of cases after CVS or amniocentesis,
with trisomies of chromosomes 13, 18, and 21 being seen in 49% of cases and other
chromosomes being affected in 51% of cases [15].
Cytogenetic testing has been increasingly supplemented in recent years by quickly
developing molecular genetic methods and has even been replaced in some cases.
The resolution of karyotyping using a microscope is 5–10 megabases (Mb) but is less
than
100 kilobases (Kb) in microarray analysis (comparative genomic hybridization). In
this way
the diagnosis of numeric aberrations (other than triploidy) as well as the detection
of
submicroscopic chromosomal imbalances (microdeletions and duplications, known as
pathological copy number variations – CNVs) are possible.
Although it is recommended in numerous countries to perform microarray analysis as
the
first examination (first tier test) after prenatal diagnostic puncture [16], Germany requires a sequential approach (karyogram before microarray
analysis).
In the case of mental retardation, autism, epilepsy, dysmorphic syndromes, and other
abnormal findings, pathological CNVs (microdeletions and duplications) are found postnatally
by microarray in up to 15% of cases.
In the case of abnormal ultrasound findings in fetuses with a normal karyogram, the
findings of the microarray analysis are abnormal in 6–8% of cases and in approximately
1% of
fetuses with unremarkable ultrasound [17]
[18]
[19]
[20].
A CNV does not always represent a pathological change. CNVs are categorized as “benign
CNV” (benign polymorphism), “probably benign CNV”, “pathological CNV”, “CNV of unclear
clinical relevance”, and “probably pathogenic CNV”. The following methods are used
to
differentiate a CNV: Evaluation of the genes in the region, comparison with databases
containing mapping of known CNVs, examination of the parents with respect to a “de
novo”
change, and comparison with the fetal phenotype.
The Danish Fetal Medicine Study Group showed that, in the case of an indication for
diagnostic puncture for a risk of ≥ 1:300 for trisomy 21 and ≥ 1:150 for trisomy 13
and 18,
approximately 5% of pregnant women are offered puncture, with a detection rate of
>
90–95% for all chromosomal aberrations being achieved. Analyses of subgroups showed
that
that rate of pathological karyograms and CNVs is higher particularly in the case of
isolated
abnormal biochemical values in first trimester screening (see [Table 2]) [21]
[22].
In the case of a nuchal translucency of > 3.5 mm and normal karyogram, CNVs are found
by microarray in 5–13% of cases [23]
[24].
Maya et al. found an increasing number of pathological CNVs (1.7%, 6.5%, and 13.8%)
as a
function of the nuchal translucency (up to 2.9 mm, 3.0–3.4 mm, and > 3.4 mm) [25].
Numerous complex malformations can be caused by monogenic diseases or single-gene
mutations, e.g., in skeletal dysplasia and other syndromes like Meckel-Gruber syndrome.
In
these cases, corresponding molecular genetic testing can be performed via next generation
sequencing (NGS). NGS panels are compilations of clinically relevant genes for a certain
clinical picture that are examined in parallel during molecular genetic testing via
next
generation sequencing (NGS). Small multi-gene panels are differentiated from large
multi-gene panels (clinical exome, clinical exome sequencing), exome sequencing (whole
exome
sequencing), and sequencing of the whole genome (whole genome sequencing).
A change from microarray analysis to exome sequencing is currently taking place
here.
These examinations are increasingly included in the workup of abnormal sonographic
findings in Germany. The catalog of indications is currently changing so that the
method and
the scope of genetic analysis should be discussed in the individual case with the
human
genetic center performing the analysis.
A method-specific feature of the genetic result of CVS is the fact that 1–2% of cases
of
mosaicism that are diagnosed are limited to extraembryonic tissue in approximately
80% of
cases (confined placental mosaicism: CPM) [26]. The clinical effects of CPM with respect to reduced placental function,
intrauterine growth restriction, and unfavorable pregnancy outcome, as described in
several
studies [27]
[28]
[29] but not in others [30]
[31] or only for trisomy 16 [32], currently cannot be conclusively evaluated. True fetal mosaicism is found in 20%
of
cases [33].
In some cases, e.g. in mosaicism, the results of CVS must be compared to additional
diagnostic tests, ultrasound examinations, or amniocentesis in order to verify the
results
and to allow additional diagnostics, e.g. determination of the exact loss/gain in
deletions/duplications via microarray analysis; diagnosis of a uniparental disomy,
e.g., in
placental trisomy 15, from trophoblast cells (direct preparation). The possibility
of CVS
results requiring clarification should be thoroughly discussed prior to the examination
in
the informed consent discussion with the patient. Similar findings after amniocentesis
are
rarer but must also be clarified.
Preparation
Prior to puncture, the patient history must be taken, the pregnant woman must be examined
for puncture risk factors, an informed consent discussion and genetic counseling must
be
provided in accordance with the German Genetic Diagnostics Act and the Pregnancy Conflict
Act,
and the pregnancy must be examined on ultrasound.
Ultrasound examination checks the following: Vitality of the fetus (fetal heart rate),
fetal biometry (verification of gestational age), placenta location, amount of amniotic
fluid,
determination of the suitable puncture site, in the case of amniocentesis: amnion-chorion
fusion or separation.
If this has not yet been performed, a differentiated sonomorphological examination
(detailed diagnosis) adapted to gestational age should be performed.
Additional factors that must be taken into consideration prior to diagnostic
puncture:
-
Rhesus status: In RhD-negative mothers and RhD-positive fetuses proven by cf-DNA
analysis or in the case of a lack of a fetal cf-DNA rhesus test, anti-D prophylaxis
must
be administered after the procedure according to the valid regulations at the time
of
publication.
-
A general check of HIV, HBV, and HBC status is not recommended prior to puncture and
should only be performed in high-risk groups or in suspicious cases. The risk of vertical
transmission of HIV infection due to amniocentesis can be lowered by HAART (Highly
Active
Anti-Retroviral Therapy).
-
The transmission of HBV does not seem to be increased in HBeAg-negative pregnant
women. There is only minimal data regarding HBC infections that tends to show that
amniocentesis does not increase the risk of transmission. There is no corresponding
data
for CVS [7].
-
Diagnostic puncture in pregnant women with infections and in those in whom vertical
transmission through puncture is possible should only be performed at expert centers
with
experience with such infections in pregnancy.
-
Puncture-related antibiotic prophylaxis is not currently recommended [7].
General principles (amniocentesis, chorionic villi sampling, and
cordocentesis)
-
Generous disinfection of the skin in the region in which the procedure will be
performed and a sterile approach are required.
-
Amniocentesis does not require local anesthesia [7]. Local anesthesia can be used for CVS due to the larger needle size but is not
absolutely necessary based on the experience of the authors of this publication.
-
CVS, amniocentesis, and FBS are performed under continuous ultrasound guidance and
typically "free hand", i.e., without puncture aids. The needle is guided in the
longitudinal direction in the acoustic window. The entire needle should be displayed
on
ultrasound during the puncture procedure.
Chorionic villus sampling
Chorionic villus sampling is largely performed using a transabdominal approach but
can
also be performed using a transcervical approach depending on the position of the
placenta
or the anatomical position of the uterus (retroflexio uteri). The complication rate
for
transcervical access compared to transabdominal puncture is not significantly higher
[34]. However, transcervical chorionic villus sampling is more technically challenging
and difficult to learn. Therefore, transabdominal chorionic villus sampling is the
method of
choice.
For transabdominal CVS, various needles can be used: 18 to 21-gauge needle or more
rarely 18/21-gauge double needles.
For transcervical CVS, biopsy forceps inserted through the cervical canal or a biopsy
catheter with a guidewire can be used [7].
Suction is created with a syringe filled with culture medium mounted on the needle.
The
needle is then moved slowly forward and backward under sonographic guidance in the
chorion
thereby aspirating chorionic villi. The chorionic plate must not be damaged since
this can
result in a miscarriage. During puncture, the villi must be drawn into a tube containing
sodium-heparin to avoid blood coagulation at the villi.
Amniocentesis
The puncture needle is inserted under sonographic guidance through the mother's
abdominal wall and the uterus into the amniotic cavity and amniotic fluid is aspirated.
The
first milliliter of aspirated amniotic fluid is discarded to reduce the risk of
contamination with the mother's cells. Paraplacental access is the method of choice.
In the
case of a complete anterior placenta and transplacental puncture, the placental umbilical
cord insertion or vessels of the chorionic plate are not damaged.
In the case of chorioamniotic separation, it is recommended to delay amniocentesis
either until a later time when the amnion and chorion are fused or to select
placentacentesis.
A 20- to 22-gauge needle is recommended for amniocentesis.
Cordocentesis
Cordocentesis is performed with a transabdominal approach under continuous ultrasound
guidance preferably with a 20- to 22-gauge needle. The needle is advanced through
the
mother's abdominal wall and uterine wall into the umbilical vein. Transplacental access
to
the umbilical vein in the case of an anterior or lateral placenta is technically easiest.
Puncture of the fetal umbilical cord insertion, the intrahepatic part of the umbilical
vein,
or a free umbilical cord loop is also possible but technically more demanding due
to fetal
movement among other things. Umbilical cord bleeding occurs more frequently and for
longer
periods after puncture of a free loop [35].
In comparison, significantly shorter puncture times were seen in puncture of the
placental umbilical cord insertion, while a significantly lower rate of maternal blood
contamination was seen in puncture of a free cord loop [36].
Whether the cord insertion, the intrahepatic part of the umbilical vein, or a free
cord
loop is punctured depends mainly on the location of the placenta, the position of
the fetus,
and thus on the accessibility of the umbilical vein.
In the case of puncture of the placental cord insertion, it is recommended to verify
the
fetal origin of the blood. This is performed by analyzing the concentration of the
fetal
hemoglobin – HbF – or by determining the mean corpuscular erythrocyte volume – MCV.
Diagnostic puncture in multiples
Puncture in multiples should only be performed by experts and centers with a high
level
of experience.
One advantage of CVS compared to amniocentesis in multiples is that the procedure
is
performed earlier in the pregnancy. Thus, in the case of a pathological result with
indication for a selective reduction, this can also be performed at an earlier point
in time
and with a lower risk of miscarriage [37].
The planning of diagnostic puncture in multiples requires determination of the
chorionicity and amnionicity.
Each placenta must be precisely assigned to the corresponding fetus. The acquired
sample
must be able to be clearly assigned to the respective fetus and labeled accordingly.
Amniocentesis in dichorionic twins can be performed as a single or multiple puncture.
In
the case of a single puncture, after puncture and aspiration of the amniotic fluid
from the
first amniotic cavity, the needle is advanced through the separating wall into the
second
amniotic cavity where the second amniotic fluid sample is collected in a second syringe.
In
the case of multiple puncture, two needles (or a number of needles corresponding to
the
number of multiples) are used and the amniotic cavities are punctured separately.
The
decision as to which method is used is based on the experience of the person performing
the
procedure and also depends on the anatomic conditions.
In the case of monochorionic-diamniotic twins, puncture of one amniotic sac can be
sufficient. In the case of discordant biometric or sonoanatomic results, puncture
of both
amniotic sacs is recommended [7].
When performing CVS for dichorionic multiples, it must be ensured that chorionic villi
are acquired from each placenta. The puncture sites should be able to be definitively
assigned to the respective chorion.
In the case of monochorionic multiples, CVS can be performed as a single puncture
of the
shared chorion. In the case of discordant biometric or anatomical findings, amniocentesis
with separate puncture of the two amniotic sacs can be offered. Alternatively, in
such
cases, CVS can be performed as a multiple puncture of the chorion in the vicinity
of the
placental cord insertions.
After puncture (amniocentesis, CVS, FBS)
The fetal heart rate and the amount of amniotic fluid are checked and documented.
This
examination can be repeated several days after the puncture.
Although physical rest is typically recommended for 24–48 hours, this is not based
on
evidence. The administration of tocolytic substances after puncture does not have
a clear
benefit with respect to preventing complications [7].
Patients should be advised to seek medical attention if experiencing symptoms like
lower
abdominal pain, amniotic fluid leakage, or fever.
Complications
Maternal complications
Maternal complications after diagnostic puncture are extremely rare and are usually
limited to pain at the puncture site, small hematomas in the abdominal wall, and circulatory
dysregulation [38]
[39].
Severe maternal complications (sepsis) have been reported in individual cases and
can be
caused by puncture of the maternal bowel [7].
Injury to the fetus
Injury to the fetus is very rare with continuous ultrasound monitoring during the
procedure [40]. However, injury is possible if the needle is not completely visible. Therefore,
the
entire needle must be visible during the puncture.
Although contact between the fetus and the needle is possible during proper performance
of the procedure under continuous ultrasound guidance, it has only been reported in
individual case reports as a minor superficial skin lesion [7]
[41]
[42]
[43].
Leakage
Transient leakage of amniotic fluid can occur as a result of amniocentesis. This is
usually temporary and ceases spontaneously. Expectant management results in a live-birth
rate of over 90%. Leakage thus has a significantly better prognosis than spontaneous
premature membrane rupture [44]
[45].
Since leakage is rare, there are no recommendations for management equivalent to those
for spontaneous premature membrane rupture. Clinical practice is an approach adapted
from
spontaneous premature membrane rupture. However, there is no evidence for this.
Puncture-related miscarriage
The calculation of the risk of miscarriage after diagnostic puncture is based on the
probability of natural loss of a pregnancy, i.e., spontaneous abortion (background
risk).
The probability of a spontaneous abortion is primarily dependent on gestational age.
Further
factors that increase the risk for spontaneous abortion are maternal characteristics,
e.g.,
maternal age, preexisting conditions, and obesity [46]. Pregnancy-related factors, like fetal anomalies and genetic aberrations of the
fetus, also increase the risk for miscarriage. Some laboratory parameters are indicative
of
an increased miscarriage rate. A lower concentration of PAPP-A is associated with
an
increased risk for spontaneous abortion [41]
[46]
[47]
[48]
[49]
[50], ([Table 3]).
Table 3 Risk factors for miscarriage [7]
[43]
[46]
[49]
[51].
|
* In the case of prior acute or transient vaginal bleeding or vaginal infection,
puncture should be delayed by 2–4 weeks depending on the course.
|
|
Maternal
-
Vaginal bleeding before or during puncture/hematoma (contraindication for
puncture)*
-
Symptomatic vaginal infection (contraindication for puncture)
-
Hypertension
-
Obesity
-
Multiparity (more than 3 births)
-
Prior history of 3 or more abortions
-
Nicotine abuse
|
|
Pregnancy-specific
-
Abnormal sonographic finding
-
(increased NT, fetal malformation, growth retardation)
-
Chromosomal aberration
-
Abnormal serum screening (elevated AFP, low PAPP-A)
|
The individual background risk greatly influences the possibility of a miscarriage
after
diagnostic puncture. When evaluating the puncture-related miscarriage risk, the a-priori
risk for a spontaneous abortion must therefore be taken into consideration. Cohorts
with and
without diagnostic puncture with a comparable a-priori risk are ideally compared to
one
another.
The study data on miscarriages after amniocentesis, CVS, and FBS varies due to this
individual background risk but also due to study-specific factors (including the
completeness of the data regarding the further course of the pregnancy, presence of
control
groups, randomization, duration of follow-up, time of the procedure, comparison of
low-risk
and high-risk groups for chromosomal aberrations and other genetic diseases, inclusion
or
disregarding of the background risk).
Amniocentesis and chorionic villi sampling
Amniocentesis and chorionic villi sampling
Current publications since 2015 show that the miscarriage risk after amniocentesis
and CVS
performed in expert centers is not significantly higher than the spontaneous abortion
rate
[2]
[3]
[5].
In the Danish national cohort study by Wulff et al. in 2016 [3], 5,072 CVS procedures and 1,809 amniocentesis procedures were analyzed using
propensity score matching in a total of 147,987 pregnant women after first-trimester
screening. The miscarriage risk was not higher after diagnostic puncture than in the
control
group.
A similar result was seen in a meta-analysis by Akolekar et al. (2015) [2], including 21 studies (14 amniocentesis studies and 7 CVS studies) each with at
least
1000 punctures published after the year 2000. The procedure-based weighted miscarriage
risk
was 0.11% for amniocentesis and 0.22% for CVS.
A current meta-analysis, an update of the publication by Akolekar in 2015 [2], analyzed 12 controlled studies including a total of 63,723 amniocentesis procedures
(control group 330,469 without amniocentesis) and 7 studies with a total of 13,011
CVS
procedures (control group 232,680 without CVS) [5]. The weighted miscarriage rates were 0.3% (amniocentesis) and 0.2% (CVS). Analysis
of
studies on pregnant women with a comparable risk profile showed procedure-related
miscarriage
rates of 0.12% (amniocentesis) and 0.11 (CVS). This study emphasizes the influence
of the
comparison of inhomogeneous study groups on miscarriage rates after amniocentesis
and
CVS.
The ACOG (American College of Obstetricians and Gynecologists) included the results
of the
current studies on miscarriage rates after amniocentesis and CVS (0.11% for amniocentesis,
0.22% for CVS) in the Practice Bulletin published in 2016 [51].
A retrospective study by Gil et al. [50] analyzed the procedure-related miscarriage risk after CVS with propensity score
matching. The authors conclude that the procedure-related risk is low in the low-risk
collective for aneuploidy and comparable to that of the group without CVS. Since
pregnancy-related and demographic characteristics affect the procedure-related risk,
these
should be taken into consideration when counseling pregnant women (see [Table 3]).
Older studies from the 1970s and 1980s specifying a miscarriage risk of 0.5–1% [52]
[53]
[54]
[55] no longer correspond to current conditions.
Today, diagnostic puncture in prenatal medicine is performed under continuous ultrasound
guidance. Consequently, the rate of procedure-related miscarriage is significantly
lower [40] and so is the rate of fetal injuries and blood in the aspirated specimen.
The image quality of current ultrasound devices has improved significantly, consequently
allowing puncture with higher precision.
In addition, the current criteria for ruling out puncture, e.g. bleeding, are
stricter.
In summary, based on the data from the more recent literature regarding the miscarriage
rate after amniocentesis or CVS, the following can be stated:
-
In centers with a high level of puncture experience, the procedure-related miscarriage
risk after diagnostic puncture is not statistically significantly different from the
rate
of spontaneous abortion (0.11% for amniocentesis, 0.22% for CVS).
-
The results from more recent literature must be correctly included when counseling
pregnant women on prenatal diagnostics so that they can make informed decisions.
-
Examiners performing diagnostic puncture should have an overview of the further course
and outcome of the pregnancy (follow-up) so that this information can be used as the
basis
for the counseling of pregnant women (see the section on quality control).
-
During the informed consent discussion for pregnant women, special factors, like fetal
anomalies, chorioamniotic separation, bleeding, retrochorionic hematomas, etc. should
be
taken into consideration as risk factors (see [Table 3]).
Fetal blood sampling
The miscarriage risk after FBS has been examined in multiple studies. There may be
a
higher miscarriage risk after FBS than after amniocentesis and CVS. The published
miscarriage
rates are between 0.4% and 1.4% [56]
[57]
[58]
[59].
A current study retrospectively analyzes 6290 FBS procedures and shows a procedure-related
increase in the miscarriage rate of 0.6% compared to a control group (1.6% vs. 1.0%).
The
authors of this study define transplacental puncture, prolonged bleeding (> 1 minute),
and
fetal bradycardia (fetal heart rate < 100/min, > 1 minute) as risk factors for
miscarriage [60].
Further consequences of FBS can be umbilical cord bleeding and fetal bradycardia.
Both
complications usually resolve spontaneously [56].
However, the comparability of studies on complications after FBS is limited by the
low
number of cases and the heterogeneity of the study collectives and the indications.
Since FBS is restricted to several centers in Germany, pregnant women requiring FBS
are
also informed with respect to the center-specific outcome. According to the authors
of this
article, the complication rate after FBS is lower than described in the literature.
Multiples
Studies on miscarriage rates in multiples have an inhomogeneous result compared to
current studies on singleton pregnancies. In addition, there is little data examining
the
procedure-related risk of miscarriage in the context of background risk. However,
the
results of current studies indicate that the procedure-related risk of miscarriage
is not or
is only minimally higher than the background risk [61]
[62]
[63]
[64].
Multiple randomized studies hypothesize that puncture in the case of multiples is
not
associated with a higher miscarriage rate [65]
[66]
[67].
A meta-analysis of 16 studies including 3419 twin pregnancies with amniocentesis and
2517 without amniocentesis did not show a significant difference between pregnancies
with
and without amniocentesis. The pooled miscarriage rate in both groups was 2.4% [62].
A multicenter study that used multivariate regression to examine the relationship
between CVS and miscarriage in twin pregnancies showed double the risk for miscarriage
in
the group with CVS compared to the group without CVS [68]. The authors attribute the increase in the miscarriage risk after CVS primarily
to
the influence of different factors and not to the procedure itself. These factors
are:
maternal obesity, monochorionicity, biometric discordance between twins, and increased
NT.
One study including 8581 twin pregnancies with 445 CVS procedures using propensity
score
matching also shows that the procedure-related risk of miscarriage is largely dependent
on
risk factors. These are mainly the factors that are also the indication for CVS [69]. In comparison to groups with a low risk for spontaneous abortion, the authors of
this multicenter study found an increase in the rate of miscarriage of 3.5% after
CVS.
The selection of the puncture method (single or multiple puncture) does not seem to
affect the miscarriage rate [70]
[71].
Alloimmunization
According to older studies, feto-maternal bleeding after amniocentesis and CVS can
trigger alloimmunization against fetal blood group antigens in approx. 1% of cases
[55]
[72].
Rh-negative women pregnant with RhD-positive fetuses who did not receive anti-D
prophylaxis were examined in a Danish cohort study. There was a very low rate of
immunization (none in 189 amniocentesis procedures and 1 in 543 CVS procedures) [73].
Nonetheless, anti-D prophylaxis is currently recommended after puncture when the fetal
RhD status is positive or unknown.
Only in the case of an RhD-negative partner and reliably verified paternity can anti-D
prophylaxis be omitted. In these cases, the blood group of the partner should be
documented.
Unsuccessful puncture
In the case of unsuccessful amniocentesis (“dry tap”), puncture at another location
can
be performed. However, more than two punctures per session are not recommended due
to the
significant increase in the risk of miscarriage [74]. It is recommended to stop the procedure after two unsuccessful puncture attempts
and to refer the pregnant woman to a facility with greater puncture experience.
Further complications
Further extremely rare complications include amnion separation, bleeding into the
amniotic cavity, and formation of a retrochorionic hematoma.
Informed consent
The currently valid legal requirements must be taken into consideration. Puncture
with the
goal of analyzing genetic properties of the fetus is subject to the law on genetic
testing in
humans (German Genetic Diagnostics Act) dated 7/31/2009.
According to the Patients' Rights Act that went into effect in 2013, pregnant women
have a
right to comprehensive information about all available and necessary examinations,
diagnoses,
and treatments. The content of the law regarding the prevention and management of
pregnancy
conflicts (Pregnancy Conflict Act) must be taken into consideration.
Documentation
Documentation of diagnostic puncture should include the following information:
-
Findings from which the indication for diagnostic puncture arises
-
Documentation of the informed consent discussion prior to puncture including the
written informed consent of the pregnant woman for the examination
-
Documentation of the ultrasound examination prior to the procedure (see above)
-
Documentation of the procedure: instrument being used, puncture site, number of
punctures, sample amount, appearance of the amniotic fluid sample
-
Documentation of the vitality of the fetus and the amniotic fluid amount after the
procedure and possible indications of early complications (see above)
-
Documentation of anti-D prophylaxis (incl. the lot number)
-
Documentation of the procedure in the maternity passport
-
Documentation of consent to participate in a genetic study in accordance with the
German Genetic Diagnostics Act.
Quality control
The goal of each diagnostic puncture in prenatal medicine is to acquire an adequate
amount of the material needed to answer the particular medical question and to prevent
complications. This can only be ensured if the examiner is highly qualified.
There is an association between the complication rate after prenatal diagnostic puncture
and the examiner’s experience measured based on the number of procedures performed
annually
[75]. However, the number of procedures needed to ensure adequate quality varies greatly
in the literature. It is currently not possible to specify an evidence-based minimum
number
of procedures to be performed annually for quality assurance since the relevant data
in the
literature varies greatly [76]
[77]
[78]
[79]
[80]. According to the recommendations of the Royal College of Obstetricians and
Gynecologists (RCOG), at least 30 procedures per year with continuous review are required.
The RCOG requires at least 100 procedures per year for experienced examiners [81].
Training and specialist training
Diagnostic puncture training should begin with model/simulator training in which the
needle is guided in the ultrasound window so that the entire needle up to the tip
remains
visible and the intended target is reliably reached.
Once model-based training has been mastered, clinical training should begin with
"simple" amniocentesis procedures.
This includes procedures performed in geriatric pregnancies (e.g. amnion drainage),
procedures in posterior placenta, and procedures in the case of a sufficient amount
of
amniotic fluid.
The number of procedures needed to master the procedure varies in the literature and
ranges between 30 and 400. However, no improvement is able to be identified after
100
procedures [78]
[80]
[81].
